The objective of the research is understanding of the CNS structures and processes underlying associative learning. Our method involves electrophysiological recording of multiple-unit activity during avoidance conditioning of intact rabbits implanted with chronic microelectrodes. In previous studies we observed acquisition of CS-contingent neuronal activity in parallel with CR-acquisition. The neuronal activity showed associative properties (e.g., stimulus control) and behavior-independence. Behavior-independence was shown by: (a) by presence of neuronal stimulus control despite absence of behavioral control, due to a "ceiling effect." The proposed studies are intended to determine: (a) the duration of retention of the persistent neuronal activity; (b) which category of retention phenomenon (between-session extinction or savings) is reflected by the neuronal activity; and (c) the relationship of the neuronal activity observed in the initial study to the occurring in related CNS structures. We hope that this work will bear on the neurophysiological basis of the learning performance distinction.